1. Field of the Invention
This invention relates to improvements in the heater head assembly of a heated-gas engine, particularly a Stirling engine. The heater head assembly is of the type having a bundle of heater tubes connecting a cylinder to a regenerator housing via a manifold on either the cylinder side, regenerator housing side or on both the cylinder and regenerator housing sides.
2. Description of the Prior Art
In a Stirling engine, fuel injected from a spray nozzle is mixed with air and the air-fuel mixture is combusted in a combustion chamber. A bundle of heater tubes constituting part of the engine heater head assembly and linking a cylinder with the housing of a regenerator are heated by the combustion gas before the gas is discharged from the combustion chamber. In a typical configuration, the heater tubes are connected at one end to a manifold on the cylinder side and at the other end to a manifold on the regenerator housing side. A working gas sealed within the heater tubes reciprocates between the cylinder and regenerator housing via the manifolds and picks up the thermal energy given off by the combustion gas in the combustion chamber. In order to achieve a uniform flow rate distribution of the working gas which flows into the heater tubes, flow straightening vanes are provided near manifold connection ports where the manifolds are connected to the cylinder and regenerator housing.
The prior-art heater head assembly of this type involves a number of problems which stem from the particular connection configuration between the manifolds and the cylinder or regenerator housing. Specifically, the portion of each manifold where the connection is made defines a flow passage which is constricted on the cylinder or housing side and of considerably larger width on the heater tube side. These connection portions magnify the influence of working gas inertia and causes a sudden change in the direction of working gas flow, particularly when the engine is operating at high speed. Since such a change in flow direction meets considerable resistance, there is greater pressure loss and a flow rate distribution which favors the heater tubes at both ends of each manifold. The end result is a decline in engine output.
Another disadvantage of the conventional heater head assembly is that the manifolds are formed separately of the cylinder and regenerator housing and must be welded to these units while maintaining strict positional accuracy. This is followed by drilling holes into the manifolds so that the ends of the heater tubes may be inserted. Such a construction entails numerous manufacturing steps, higher machining costs and a number of welds which can have a deleterious effect upon reliability and durability.
A further drawback encountered in the prior art is the necessity of the flow straightening vanes. These require the drilling of holes in the manifolds so that the vanes may be installed, followed by welding work for installation. High machining costs and reliability problems are the result.